RE: End System PMTUD behavior question

Many thanks for the information. Could you tell me the OS variants on the hosts and router? Also, do you have any tests involving applications?  I will send you an off-line e-mail to discuss possible additional testing.

Best Regards, 

Jeffrey Dunn 
Info Systems Eng., Lead 
MITRE Corporation.
(301) 448-6965 (mobile)

-----Original Message-----
From: Thomas Peterson [mailto:thomasp@iol.unh.edu] 
Sent: Thursday, January 22, 2009 3:38 PM
To: Dunn, Jeffrey H.
Cc: Rémi Denis-Courmont; ipv6@ietf.org; Huang, Frank; Sherman, Kurt T.; Liou, Chern; steve_eiserman@uscourts.gov; ipv6-bounces@ietf.org; v6ops@ops.ietf.org; Grayeli, Parisa
Subject: Re: End System PMTUD behavior question

Hi Jeffrey,

I have attached a picture which shows one of the topologies we use for  
our PMTUD tests.

In this test case we transmit an Echo Request from REF-Host2 to TAR- 
Host1 with a packet size of 1500 bytes. REF-Host2 fragments the Echo  
Request it transmits. TAR-Host1 replies to this Echo Request with an  
Echo Reply to REF-Host2 with a size of 1500 bytes that is not  
fragmented. TAR-Router1 sends a Packet Too Big message in response as  
this Echo Reply is too large to forward onto Network 2.

In all of the cases we have seen TAR-Host1 does fragment future Echo  
Replies to REF-Host2, however, it does not retransmit any Echo Replies  
for Echo Requests received prior to receiving the Packet Too Big  
message from TAR-Router1.

Additionally from the tests we have performed in our lab if TAR-Host1  
were to send an Echo Request with a packet size of 1500 bytes TAR- 
Router1 would send a Packet Too Big message in response. In all cases  
we have seen TAR-Host1 would not re-transmit this Echo Request and  
this would be counted as packet loss in the ping command results.

If this does not ideally match your test scenario we'd be happy to  
work together off-line to replicate your scenario.

Thanks,
Tom

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